Are there any RFCs for address selection for IPv4

[Gary Jennejohn]

On Sun, 25 Apr 2021 18:20:37 +0800
Zhenlei Huang <zlei.huang at gmail.com> wrote:

> Hello hackers,
> 
> For IPv6 there's RFC 6724 to clarify the default address selection procedure, 
> both for source address selection and destination address selection. Are there
> any RFCs like RFC 6724 that are for IPv4? 
> 
> I'm exploring RFC 3927, consider this situation, a host configured with link-local
> address on NIC and global unicast alias address on loopback interface, and default route to 
> the link-local address of router (some ISPs do this). The current implementation kernel
> will use the link-local address as the source address when initializing a connection to 
> remote host via the default route. It seems wrong, as link-local address are not 
> routable as per RFC 3927.
> 
> So it is important if there's corresponding RFC clarify the source address selection 
> for IPv4.
> 
> Thanks :)
>

I'm no expert on this, but the router must have a public, routable adress
to the internet, otherwise it can't function as a router.  This address
is (usually) provided by the ISP.

It's using its pubic address to route packets to the internet and very
probably NAT to handle packets from and to the LAN.

So, the internal LAN does not have to use routable addresses.

-- 
Gary Jennejohn